A method for flowable oxide deposition is provided. An oxygen source gas is increased as a function of time or film depth to change the flowable oxide properties such that the deposited film is optimized for gap fill near a substrate surface where high aspect ratio shapes are present. The oxygen gas flow rate increases as the film depth increases, such that the deposited film is optimized for planarization quality at the upper regions of the deposited film.
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1. A method of forming a dielectric film comprising:
depositing a flowable oxide on a semiconductor structure in a first phase having a first oxygen flow rate for a first time interval, wherein the first oxygen flow rate is zero;
depositing a flowable oxide on a semiconductor structure in a second phase having a second oxygen flow rate for a second time interval;
depositing a flowable oxide on a semiconductor structure in a third phase having a third oxygen flow rate for a third time interval, wherein the second oxygen flow rate is greater than the first oxygen flow rate, and wherein the third oxygen flow rate is greater than the second oxygen flow rate.
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The present invention relates generally to semiconductor fabrication and, more particularly, to methods of forming a dielectric film.
In order to provide integrated circuits (ICs) with increased performance, the characteristic dimensions of devices and spacing on the ICs continue to be decreased. Fabrication of such devices often requires the deposition of dielectric materials into features patterned into layers of material on silicon substrates. In most cases, it is important that the dielectric material completely fill such features. Filling such narrow features, so-called gap filling, places stringent requirements on materials used, for example, for pre-metal dielectric (PMD) applications. The pre-metal dielectric layer on an integrated circuit isolates structures electrically from metal interconnect layers and isolates them electrically from contaminant mobile ions that degrade electrical performance. PMD layers may require filling narrow gaps having aspect ratios (that is the ratio of depth to width), of five or greater. Dielectric films play an important role in the fabrication of semiconductor devices. It is therefore desirable to have improved processes for the deposition of dielectric films.
In a first aspect, the present invention provides a method of forming a dielectric film comprising: depositing a flowable oxide on a semiconductor structure in a first phase having a first oxygen flow rate for a first time interval; depositing a flowable oxide on a semiconductor structure in a second phase having a second oxygen flow rate for a second time interval; depositing a flowable oxide on a semiconductor structure in a third phase having a third oxygen flow rate for a third time interval, wherein the second oxygen flow rate is greater than the first oxygen flow rate, and wherein the third oxygen flow rate is greater than the second oxygen flow rate.
In a second aspect, the present invention provides a method of forming a dielectric film comprising: depositing a flowable oxide on a semiconductor structure in a first phase having a first oxygen flow rate for a first time interval; depositing a flowable oxide on a semiconductor structure in a second phase having a second oxygen flow rate for a second time interval; depositing a flowable oxide on a semiconductor structure in a third phase having a third oxygen flow rate for a third time interval, wherein the first oxygen flow rate is zero, and wherein the second oxygen flow rate and the third oxygen flow rate increase based on a piecewise linear function.
In a third aspect, the present invention provides a method of forming a dielectric film comprising: depositing a flowable oxide on a semiconductor structure, wherein oxygen gas is flowed at a monotonically increasing flow rate up to an upper flow limit.
Certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines which would otherwise be visible in a “true” cross-sectional view, for illustrative clarity. Furthermore, for clarity, some reference numbers may be omitted in certain drawings.
Features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which:
Exemplary embodiments will now be described more fully herein with reference to the accompanying drawings, in which exemplary embodiments are shown. Embodiments of the present invention provide an improved method for flowable oxide deposition. An oxygen source gas is increased as a function of time or film depth to change the flowable oxide properties such that the deposited film is optimized for gap fill near a substrate surface where high aspect ratio shapes are present. The oxygen gas flow rate increases as the film depth increases, such that the deposited film is optimized for planarization quality at the upper regions of the deposited film.
It will be appreciated that this disclosure may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. For example, as used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms “a”, “an”, etc., do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including”, when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Reference throughout this specification to “one embodiment,” “an embodiment,” “embodiments,” “exemplary embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “in embodiments” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms “overlying” or “atop”, “positioned on” or “positioned atop”, “underlying”, “beneath” or “below” mean that a first element, such as a first structure (e.g., a first layer), is present on a second element, such as a second structure (e.g. a second layer), wherein intervening elements, such as an interface structure (e.g. interface layer), may be present between the first element and the second element.
As used herein, the term “flowable oxide” is a flowable doped or undoped silicon oxide film having flow characteristics that provide consistent fill of a gap. The flowable oxide film may also be described as a soft jelly-like film, a gel having liquid flow characteristics, a liquid film, or a flowable film. The flowable oxide deposition methods described herein are not limited to a particular reaction mechanism (e.g., the reaction mechanism may involve an adsorption reaction, a hydrolysis reaction, a condensation reaction, a polymerization reaction, a vapor-phase reaction producing a vapor-phase product that condenses, condensation of one or more of the reactants prior to reaction, or a combination of these). The substrate is exposed to the process gases for a period sufficient to deposit a flowable film to fill at some of the gaps. The deposition process typically forms soft jelly-like film with good flow characteristics, providing consistent fill. However, flowable oxide films may suffer from poor planarization quality (PQ). After deposition of the film is complete, it is often desirable to planarize the film to a desired depth. Therefore, the flowable oxide film may be prone to “dishing” such as shown by region 211 of
Embodiments of the present invention provide a dielectric formation method that utilizes flowable oxide in a single deposition process with a single planarization process. The method provides a flowable oxide that has good gap fill properties, and also has good planarization quality. The gap fill quality is most critical near the base of a high-aspect ratio feature, where gap fill may be difficult. Reducing or omitting oxygen gas flow into the deposition tool reaction chamber during the initial stages of deposition allows the flowable oxide to retain the good gap fill capabilities. As the depth of the flowable oxide increases, and exceeds the height of the high aspect ratio features, the planarization quality (PQ) becomes more important. At a higher depth, the flow of oxygen gas is increased. The effect of increased oxygen gas on the flowable oxide decreases the gap fill quality, but increases the PQ. However, with the depth of the flowable oxide exceeding the height where deep gaps exist, the gap fill properties are not as important, while the planarization quality becomes more important. Hence, embodiments of the present invention mitigate the tradeoff between gap fill quality and planarization quality, allowing a single deposition process to be used for a pre-metal dielectric film, saving considerable manufacturing cost over prior art methods.
Increasing the oxygen gas flow creates a more dense SiO2 film, hence changing the properties of the flowable oxide. In particular, the viscosity of the flowable oxide is increased, which increases the planarization quality, while decreasing the gap fill quality. Embodiments of the present invention exploit this relationship to use little or no oxygen initially, to have good gap fill quality near the substrate surface, where high aspect ratio shapes are present, and increase the flow of oxygen as the deposition film height increases, where there are no high aspect ratio shapes, but the planarization quality becomes important.
f=K(1+t−t1)2
Where f is the flow rate, and K is a constant, and t is the current time in seconds. In some embodiments, the constant K may range from about 0.2 to about 0.3. In some embodiments, the difference between time t1 and time t2 may be about 15 seconds, and the difference between time t2 and time t3 may be about 10 seconds. In one embodiment, the value of K is 0.25, and the difference between time t2 and t1 is 10 seconds, and the difference between time t3 and t1 is 25 seconds, such that, at time t2, the current flow rate of oxygen gas f1 may be derived by:
f1=0.25(11)2=30.25 sccm
And at time t3, the current flow rate of oxygen gas f2 may be derived by:
f2=0.25(26)2=169 sccm
The controller 818 may be coupled to a deposition tool 830 which may be a chemical vapor deposition tool (CVD) suitable for deposition of flowable oxide. The controller may receive input data 810. Input data 810 may include recipe parameters for depositing flowable oxide in accordance with embodiments of the present invention. Embodiments of the present invention may further include a computer program product embodied in a non-transitory computer-readable medium that implements the multiple phases of deposition as illustrated in
The controller 818 may also generate output data 814. The generated output data 814 may include deposition simulation data, such as computed flow rates and time durations of each phase to achieve a desired dielectric film quality and thickness under certain process conditions.
While the invention has been particularly shown and described in conjunction with exemplary embodiments, it will be appreciated that variations and modifications will occur to those skilled in the art. For example, although the illustrative embodiments are described herein as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events unless specifically stated. Some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the invention.
Liu, Huang, Liu, Hung-Wei, Chen, Tsung-Liang, Sun, Zhiguo
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